This invention relates to a failure detection sensor, a failure detection system, and a structure, which are suitably applied, for example, to detect the risk of the failure of joints of various structures such as buildings.
For the purpose of joint (wide sense joint including connection and fastening) of structural members of various structures such as buildings, bridges, and tunnels, various joint technologies such as welding, rivets, bolts and nuts have been used. Since the failure of the joints of the structural members has a close relation to damage of the structure from the view of safety of the structure, it is necessary to examine damage of joints and a periodic examination must be made. Conventional general examination methods for this purpose are mainly a hammering test and visual inspection. However, especially the hammering test requires intuition and skill of inspectors, and therefore the inspectors are limited. Furthermore, generally, the joints of the structural members frequently locate at a high place or a place which is difficult to be seen by persons, so it is very difficult to carry out the hammering test and visual inspection. Also, examination work using a high place working car is an inefficient work which needs time and energy and the risk is high. Therefore, demanded is a technology which detects and notifies the risk of the failure of the joints in a short time and completely automatically around the clock.
For this purpose, known is a watching method which detects immediately when fracture of bolts fixing an object occurs or an object fixed falls off (see patent literature 1). According to the watching method, the state of the bolts fixing the object or the object attached to the structure is always watched contactless, and when fracture of the bolts occurs or the object attached falls off, it is immediately detected and an alarm is caused. Furthermore, known is an axial force control bolt which can fasten an object to be fastened with a predetermined axial force or an axial force reaching a plastic region and easily know whether the bolt is of before plastic deformation or after plastic deformation (see patent literature 2). The axial force control bolt comprises an axial part and a screw part and can control the axial force applied in the axial direction. Axial force detecting materials which fracture when the strain in the axial direction of the bolt exceeds a predetermined value are applied to the outer surface of at least the axial part of the bolt. The axial force detecting materials are applied in the state where the tension in the axial direction is applied to the bolt in advance. In addition, known is a high strength bolt having the capability of preventing scattering, provided with materials in the inside of the high strength bolt in the axial direction which can be elongated larger than the materials of the high strength bolt and have a cross section gradually increasing from the position near the end surface to the end in respective ends (see patent literature 3).